There are many applications of precision motion sensors, and in particular, the field of accelerometers and servos depend heavily on the accuracy and high bandwidth capability of these sensing devices. Linearity of motion of the moving stage and linearity of spring rates are two important characteristics that influence performance. The performance along the direction of sensing is often called on-axis performance and the degradation in performance due to forces along directions other than the direction of sensing is called off-axis or cross-axis contamination.
A sensor is usually mounted on a stage that moves relative to a stationary base. The moving stage is suspended through some linear bearing or linear movement flexure arrangement from the base so as to provide the degree of freedom the stage requires for sensing while blocking or restraining the stage from moving in other off-axis directions. Attempts at trying to improve the on-axis performance typically suffer from off-axis (or cross-axis) contaminations in the process. They also suffer from non-linearity in stage movement and/or in the spring rate. Servo bandwidth gets limited at higher frequencies due to higher order structural resonance modes containing off-axis motion components. Ideally a linear flexure bearing has finite stiffness in the direction of desired motion and infinite stiffness in all other (off-axis) degrees of freedom.
These issues become much more predominant in the high end sensors, such as strategic grade Inertial Measurement Units (IMUs) and in high-bandwidth, ultra-precise linear servo mechanisms. The system needs to address the off-axis contamination and non-linearity issues while trying to improve the precision in the direction of sensing. The performance of the IMUs and that of the high end servo mechanisms that exist today suffer from the significant presence of higher order modes and lowering of the mode frequencies as well as non-linearity caused by stiffness and other factors leading to poor off-axis performance and lower effective usable bandwidth.